1. Technical Field
The present invention relates generally to computer-aided manufacturing of dental items.
2. Background of the Related Art
Traditionally, a dental restoration is produced in a four step process. The first step is performed by the dentist where the area to receive the restoration is prepared using various dental tools. The second step involves taking an impression of the prepared area as well as the opposing dentition in the bite position, and sending the preparation impression to a dental laboratory (as a set of upper and lower molds), along with specifications of the kind of restoration desired. The third step occurs at the dental laboratory where two models are poured and combined into an articulator, and now accurately represent the patient's dentition in the relevant area. The articulated model (made out of some hard material) shows the prepared area and adjacent teeth, as well as the opposing teeth. The fourth step involves the manufacturing of the restoration according to the specifications provided by the dentist, and ensuring that the restoration fits on the model and does not interfere with the adjacent or opposing dentition. This is done by the laboratory technician placing the restoration in progress onto the preparation model in the articulator and making sure that there is no interference when the articulator is positioned into the closed position. In particular, the technician must check the fit at the margin, that the contacts with the neighboring teeth are correct, and that the occlusion is correct.
Recently, there have been steady advances in the use of CAD/CAM technologies in the dental laboratory. Instead of creating the restoration out of some time honored technique (such as a lost wax casting technique), the restoration may be totally or partially machined in a milling machine or created in a 3D printer. There may or may not be a process of stacking porcelain onto the created substructure. These techniques, however, typically include the step of digitizing the model, and the created restoration may still be placed on the model to check the contacts and the occlusion.
With the advent of the CAD/CAM systems in the dental office, however, a new wrinkle arises. An in-office CAD/CAM system may include a milling machine, which enables the dentist to design and mill the restoration while the patient is there, and place the restoration in a single office visit. If this process is used, however, the workflow of the dentist may be disrupted, because now substantial time needs to be allocated to design the restoration while the patient is waiting. Even with a large amount of automation, there may be some proportion of dentists who do not desire the additional complication, and would rather continue to use the dental labs. However, there is still much time and material savings to capture a digital impression instead of a real impression, and to send this data to the lab through the Internet or other means. One technique for accomplishing this is described in commonly-owned U.S. Ser. No. 11/682,194, filed Mar. 5, 2007.
Once a digital impression (namely, the digital data corresponding to a 3D scan of the preparation, the mesial/distal neighbors, and the opposing occlusion) has been received by (or otherwise received at) the dental laboratory, theoretically a technician could design and mill a full contour crown just as would have been done by the dentist in the office system. Most restorations in the lab, however, are porcelain-fused-to-metal restorations, and other types of restorations which include a stronger substructure (made of metal or zirconia or some other strong material). In these cases, the technician would design a coping or framework in the CAD software, which would then be milled in a milling machine, or created in a rapid prototyping machine. After additional processing of the coping or framework (which may include sintering), the technician would then have the option of milling out a ceramic top to place on the substructure, or layer the porcelain on top of the substructure in the traditional way. As noted above, stacking porcelain is an acquired art, and the technique produces the most aesthetically pleasing restorations. To check the contacts and the occlusion, however, a hard model (that represents the preparation, the neighbors and the opposing occlusion) typically is required.
It would be desirable to provide a technique in which the hard model would not be required. The present invention addresses this problem.